1. Field of the Invention
The invention relates to a laser projector, and particularly to a laser projector performing laser raster scan using a scanning mirror.
2. Description of the Background Art
Various techniques have been proposed in connection with laser projectors for displaying clear images.
For example, in a laser projector disclosed in Japanese Patent Laying-Open No. 2007-264554, a projection optical system includes a reflection member for reflecting image light that enters the projection optical system and includes a projection image, and an imaging lens system composed of one or more lenses located on an optical path of the light reflected by a reflection surface of the reflection member. The reflection member is arranged such that the reflection surface has a variable inclination angle with respect to image light, and the imaging lens system is arranged in a variable position such that it can be located on the optical path of the reflected light changed according to changes in inclination angle. Thereby, it becomes possible to change a position of a projection target surface onto which the image is projected, and the clear image can be projected onto the projection target surface thus changed.
A laser projector disclosed in Japanese Patent Laying-Open No. 2002-328428 receives image data from a portable data processing device, emits laser light from a light source of semiconductor laser, reflects the laser light to apply it to a wall surface and changes an angle of the mirror by a mirror driver under control of a controller. The laser light is scanned two-dimensionally for projecting the image. A light receiver detects the laser light reflected by the wall surface to calculate a distance to the wall surface, and corrects the angle of the mirror according to the calculated distance. Thereby, deformation of the projected image can be corrected.
In a laser projector disclosed in Japanese Patent Laying-Open No. 2003-075768, light emitted from a light source is led by first and second light collecting lenses to a DMD (Digital Micromirror Device), is reflected by the DMD for light modulation, and the light thus modulated is projected by a projection lens. The projection lens is moved in a direction parallel to an optical axis for shifting a projection position. In synchronization movement of the projection lens, a center of the first light collecting lens is shifted with respect to an optical reference axis to change a light incident angle to the DMD. The above configuration provides a projector optical system (i.e., an optical system for a projector) that has a simple structure, is of a non-telecentric type not using a prism, allows so-called “lens shift” and uses the DMD.
A laser projector disclosed in Japanese Patent Laying-Open No. 2006-091471 includes a retardation sheet corresponding to a wavelength of light emitted from a light source, and drive means for driving the retardation sheet to change polarization of the light emitted from the light source. Thereby, the polarization of the light to which the retardation sheet is added is changed with time, and this makes it difficult to recognize speckle noises by human eyes.
A laser projector disclosed in Japanese Patent Laying-Open No. 08-015639 includes a light source, a heat ray cut-off filter for removing heat rays form light fluxes emitted from the light source, a condensing lens substantially collimating the light fluxes from which the heat rays are removed, a modified mirror type of spatial light modulation element modulating the collimated light flux according to an image signal, a projection lens projecting the reflected light incoming from the spatial light modulation element onto a screen, and a baffle that cuts off the light modulated by the spatial light modulation element except for the light reflected in the direction of its optical axis, and forms an entrance pupil of the projection lens. The modified mirror type of spatial light modulation element is configured such that, when all mirrors in this element are directed in the direction allowing entry of the light fluxes into the projection lens, the element has a certain power as a whole, and collects or converges the light fluxes diverging from the light source into the entrance pupil of the projection lens. Thereby, the image prepared by the spatial light modulation element and having a large area can be projected and displayed without increasing the optical system.
According to the techniques in the foregoing five publications, however, the laser projector emits the parallel rays of laser light so that the following problem arises.
Referring to FIG. 6, laser projector 99 emits and projects parallel rays onto a screen. A beam diameter on the screen is D independently of a distance between the screen and the laser projector.
However, when a distance from the screen to laser projector 99 is long, a display size of a projected image on the screen is large. Consequently, a space occurs between the emitted beams to cause irregularity in brightness of the projected image.
Conversely, when the distance between the screen and laser projector 99 is short, the display size of the projected image on the screen is small. Consequently, the emitted beams overlap together to reduce a resolution of the projected image on the screen.